Mitt Romney drew fire from the left Friday when he invoked a long-debunked, bias-tinged conspiracy theory on President Barack Obama's birth at a rally in Michigan

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Mitt Romney alluded to a long-debunked conspiracy theory when he told a crowd in a Detroit suburb Friday that nobody had ever asked to see his birth certificate.

Updated at 7:54 PM CST on Friday, Aug 24, 2012

Wading into a debunked conspiracy theory, Mitt Romney raised the issue of President Barack Obama's citizenship Friday by joking that "no one's ever asked to see my birth certificate."

At a rally in the suburbs of Detroit, Romney told a crowd of about 5,000 that he and his wife were happy to be back near their childhood home. "They know that this is the place that we were born and raised."

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The remark was a clear reference to the discredited claims that Obama was not born in the United States and thus ineligible to be president. Hawaii officials have repeatedly verified Obama's citizenship, and courts have rebuffed lawsuits over the issue.

The Obama campaign decried the remark, saying Romney was embracing "the most strident voices in his party instead of standing up to them."

Romney was asked about his comment in a CBS interview later in the day.

"No, no, not a swipe," Romney said. "I've said throughout the campaign and before, there's no question about where he was born. He was born in the U.S. This was fun about us, and coming home. And humor, you know — we've got to have a little humor in a campaign."

But Romney's comments for the moment aligned him again with a conservative fringe that has pursued the issue. Among the most prominent Romney backers who have questioned Obama's birth in Hawaii have been developer Donald Trump.

"Throughout this campaign, Governor Romney has embraced the most strident voices in his party instead of standing up to them," said campaign spokesman Ben LaBolt. "Gov. Romney's decision to directly enlist himself in the birther movement should give pause to any rational voter across America."

Romney adviser Kevin Madden said Romney wasn't intentionally making a reference to the questions about Obama's birth certificate.

Romney was campaigning with his running mate, Paul Ryan, and with his wife Ann in Michigan, a state where Obama has been leading but that is where Romney's father, George, made his name both as a top auto executive and as governor.

Obama has been dogged throughout his presidency by question about his birthplace. He released a long form copy of his birth certificate last year, showing he was born in Hawaii in 1961.

Romney has been very careful to steer clear of the birth certificate issue, even while enthusiastically accepting support from tycoon Donald Trump. Whenever he was asked about the issue in interviews, Romney always demurred and said it was a settled issue.

Among a segment of the conservative, anti-Obama movement, the issue is a rallying cry that continues to persist despite evidence to the contrary.

For Romney, raising the issue at this point runs contrary to his campaigns goal of boosting his support among independent and undecided voters, for whom Obama's birth certificate is presumably a non-issue.